A rotary union is generally recognized as a mechanism used to transfer fluid (under pressure or vacuum) from a stationary inlet to a rotating outlet. The rotary union is generally capable of preserving and isolating a fluid connection disposed between the stationary inlet and the rotating outlet. Rotary unions are utilized in a variety of applications—from compact rotary unions for the semiconductor industry to large, rugged-duty fluid swivels for industrial applications. Additionally, a variety of materials, sealing technology, and bearing types can be incorporated.
Rotary unions generally comprise a non-rotating union part connected to an external fluid supply and a rotating union part that is or can be affixed to a rotating device and rotates together with the rotating device. Seals are generally arranged between the non-rotating union part and the rotating union part. A rotary union can be referred to as a rotating union, swivel joint, rotary valve, rotary coupling, rotary joint, rotating joint, hydraulic coupling, pneumatic rotary union, through bore rotary union, air rotary union, electrical rotary union, vacuum rotary union, and the like. The axis of rotation of the rotary union is generally co-linear with the axis of rotation of the rotating device.
Rotary unions can be designed to endure a large range of temperatures and pressures. In addition, rotary unions may integrate multiple independent flow connections (passages) and handle different types of media simultaneously. A rotary union can generally lock onto an input valve while rotating to meet an outlet. During this time fluidic media can flow into the rotary union from a source external to the rotary union and can be held within the device during its movement. This fluidic media leaves the rotary union where the valve openings meet during rotation allowing more fluidic media to flow into the union again for the next rotation. Often functioning under high pressure and constant movement a rotary union is designed to rotate around an axis.
Rotary unions can be utilized and cooperatively function with contact printing and/or coating systems. Such contact systems (also known to those of skill in the art as print cylinders) are generally formed from components that displace a fluid onto a web substrate or article from a channel positioned internally to such a print cylinder to, for example, print an image or coat a pattern onto the substrate. An exemplary print cylinder can be provided as a gravure cylinder. Such a print cylinder can be used to carry a desired pattern and quantity of ink and transfer a portion of the ink from an internally-positioned channel to a web material that has been placed in contact with the print cylinder.
In any regard, the exemplary internally-fed gravure cylinder can be used to apply a broad number and range of fluids to a web substrate at a target rate and in a desired pattern. A suitable contact printing system incorporating a gravure cylinder can apply more than just a single fluid (e.g., can apply a plurality of individual inks each having a different color) to a web substrate when compared to a conventional externally-supplied gravure printing system that only applies a single ink. Represented mathematically, the contact printing system envisioned can use a gravure cylinder (central roll) and can print X colors upon a web substrate utilizing Y printing components where X and Y are positive integers and 0<Y<X.
In an exemplary gravure system, pre-determined ink channel networks provided to each cell can typically be connected to individual color ink reservoirs disposed at the desired printing location upon the surface of the gravure cylinder. Providing a distribution system in this manner can ensure that any part of a print design disposed upon the surface of gravure cylinder and disposed any location upon the surface of the roll can be fed by a connected ink channel for a designed ink color at designed flow rate.
By convention, rotary unions are generally disposed external to the bearing that supports the shaft of the rotating device (i.e., on the bearing side opposite the rotating device so supported). This is because one of skill in the art will feed fluids into the rotating device at a position near the axis of rotation. This provides the ability to incorporate such fluid feeds into the shaft that supports the rotating device. This is the current industry standard for roll design.
Further, it is understood that high rotational (line) speeds are considered highly desirable for increased production rates. However, it was found that when currently available rotary unions, whether or not they are connected to a rotating device such as the exemplary internally-fed gravure printing system described supra, provide a fluid near the axis of rotation and are rotated at a high circumferential speed, the centrifugal force was found to create a region of low pressure (i.e., “pull a vacuum”) in the fluid passages, or the portions of fluid passages, disposed within the region of the rotary union that is proximate to the axis of rotation of the rotating union part. This region of low pressure is thought to provide three undesirable phenomena in operations where high rotational velocities are required:    1. When the rotating union part reaches a certain rotational speed, the local pressure in any channel, or portion(s) thereof, disposed within the rotating union part that are proximate to the axis of rotation is reduced below the vaporization pressure of the fluid at the local temperature. The fluid is caused to vaporize and form gas bubbles. This phenomenon can be considered to be analogous to the cavitation observed in a hydraulic pump operating at high rpm.    2. If the fluid is not deaerated properly, the size of any entrained air bubbles in the fluid will increase as the pressure drops.    3. According to Henry's law, the amount of air dissolved in a fluid is proportional to the local pressure. When a fluid transported from a position external to the rotary union to the rotary union center, the pressure exerted upon the fluid changes from atmospheric to a near vacuum. Part of this dissolved air can then released in the form of bubbles in the fluid.
According to the ideal gas law, the gas or air bubble volume is inversely proportional to the local pressure. Therefore, the size of bubbles within the fluid will increase as the rotational speed increases. This is because the pressure in the fluid passages of the rotary union located in the region near the rotational axis decreases as the rotational speed increases. These gas or air bubbles introduce difficulties in high rotational speed operations, such as printing and coating. These can include undesirable flowrates, partial blockages within the internal roll piping, noise, vibration, and damage to the piping network. The latter can be considered analogous to the damage due to cavitation caused by an impeller.
Thus, one of skill in the art will recognize that such undesired phenomena caused by these centrifugal forces such as those described supra, must be controlled to enhance the speed and performance of equipment used in material processing technologies. A design that controls and increases the performance of high-speed rotary unions is needed in manufacturing. Clearly, a design that can correlate equipment design, fluid dynamics, and high-speed manufacturing is needed.
The rotary union of the present disclosure overcomes these problems associated with the prior art by providing a rotary union for use in a fluid delivery system that is capable of transporting single or multiple fluids, reducing sealing problems, and controlling the pressure drop due to high-speed rotation of internally-fed rolls at the fluid inputs, prevents the creation of a region(s) of low pressure in an economical manner, and mitigates these effects by allowing an internally-fed rotating device to be provided with a fluid at a position other than near the axis of rotation or through the shaft supporting the rotating device. The disclosed rotary union can be modified to accommodate different numbers of flow channels, is designed to ensure efficient rotation between incoming and outgoing conduit arrangements, and provide a better placement options between the rotating device and the bearings supporting the rotating device shaft.